Cathode ray tubes are of types adaptable to a number of specialized utilizations including entertainment displays, monitor displays; direct read-out data displays, and projection displays for large screen applications. Whatever the application, optimum resolution, contrast, and brightness are among the commonly desired characteristics. During the course of tube development to enhance brightness, operational screen potentials have been increased to the present 30 to 40+KV range wherein the generation of x-rays becomes an important consideration.
For instance, in a CRT projection system, wherein high voltage tube operation is utilized in order to provide bright imagery, a separate lead glass shield is positioned between the face of the tube and the projection lens system to attenuate the x-radiation projected from the tube. In a combination of this type, there is an inherent reduction in attainable contrast and a noticeable loss in brightness due to reflection losses resultant from the front and back surfaces of the lead glass shielding member. In certain instances an 8 percent loss in brightness has been evidenced. Additionally, extra shielding provisions are often required in the system to achieve attenuation of the x-rays emitted peripherally from the screen area of the tube.
In a CRT projection system, important considerations in addition to brightness, include implosion protection, reduced glare and enhanced contrast.
These considerations, particularly implosion protection, have been met in the prior art by a transparent cover plate affixed to the CRT face by an intermediate peripherally confined adhesive material. Such, for example, is disclosed in U.S. Pat. No. 4,204,231, wherein the adhesive material is peripherally confined by a strip of pressure-sensitive tape applied around the face area in a manner to cover the jointure region thereof. Of course, such structures offer essentially no protection against the emanation of x-rays.